1. Field of the Invention
Aspects of the invention generally relate to an apparatus and method for heat processing substrates and, more particular, to a method and apparatus for minimizing contaminates within a thermal processing chamber.
2. Background of the Related Art
In the fabrication of flat panel displays (FPD), thin film transistors (TFT) and liquid crystal cells, metal interconnects and other features are formed by depositing and removing multiple layers of conducting, semiconducting and dielectric materials from a glass substrate. The various features formed are integrated into a system that collectively is used to create, for example, active matrix display screens in which display states are electrically created in individual pixels on the FPD. Processing techniques used to create the FPD include plasma-enhanced chemical vapor deposition (PECVD), physical vapor deposition (PVD), etching and the like. Plasma processing is particularly well suited for the production of flat panel displays because of the relatively lower processing temperatures required to deposit films and good film quality which results from plasma processes.
During FPD processing, proper heat processing of the film across the entire surface of the substrate is critical for the FPD to function properly. The temperature required varies depending on the type of film being processed, and the process being performed. For example, one exemplary type of flat panel display film used in the construction of FPDs is low temperature polysilicon (LTPS). Part of the LTPS process requires the LTPS film be heated to about 600xc2x0 C. to remove hydrogen from the film, whereas a similar heat treatment for amorphous silicon (xcex1-Si) film requires a substantially lower temperature of about 450xc2x0 C.
Generally, the film heating process is temperature sensitive as temperature non-uniformity may cause insufficient removal of contaminates, resulting in peeling and ablation of the film. To compensate for temperature non-uniformity heating process times must be extended. Unfortunately, extending the heating process times increases the production cost and often results in unusable films if the process is not completed.
Conventional thermal chambers provide heat processing by heating one or more substrates through a combination of thermal conduction and radiation. Unfortunately, the chamber walls and other internal chamber components provide thermal conduction paths within the chamber resulting in conductive heat losses. The conductive heat losses create a constantly fluctuating substrate-heating environment. As the temperatures are increased, conductive heat losses become more pronounced, exacerbating the heat non-uniformity within the substrate-heating environment. Moreover, conventional thermal chambers are often very large to accommodate the substrate perimeter, further exacerbating the heating issues by increasing the area and volume to be heated. For example, as the demand for larger computer displays, monitors, flat-screen televisions, and the like increases, a typical substrate may be 620 mm by 750 mm, or larger. For instance, substrates of 1 meter by 1 meter are contemplated. Typically, to compensate for the larger substrates, larger chamber volumes, and the subsequent increase in heat losses, more heating elements are used, thereby increasing the cost of the equipment, energy usage and temperature non-uniformity. As temperatures increase, copper heating elements are often employed to offset energy costs and provide efficient heating. Copper heaters are generally more energy efficient than other types of heating elements. Unfortunately, as the temperatures are increased, copper atoms from the copper heaters often escape into the thermal chamber and contaminate the film. Thus, traditional thermal chambers and heating processes do not provide acceptably uniform and contaminant-free substrate heating for an efficient and cost effective substrate heating process.
Various contaminants are produced during use of thermal chambers. Many contaminants are formed as new parts (e.g., cables, O-rings and sheet metal) are substituted into thermal chamber and initially heated. Contaminants are outgassed, created and/or vaporized while the chamber is hot. Often, contaminants are deposited as residue to chamber surfaces with the lowest temperatures. The surfaces are usually in distant regions of the chamber and are hard to reach when cleaning the chamber. Cleaning entails disassembling the thermal chamber, removing the residue from the contaminated parts and reassembling the chamber. This procedure generally can consume three days and multiple cycles are repeated to assure removal of all contaminates. Contaminates interfere with production by reducing product quality, reducing product throughput and adding cost.
Therefore, there is a need for a method and apparatus for uniformly heat processing a plurality of substrates in an efficient, contaminate-free thermal processing system. Furthermore, there is a need for a method and apparatus to confine and easily remove contaminates from the system.
Embodiments of the invention generally provide an apparatus for heating substrates, comprising a chamber having a heater disposed within the chamber with a plurality of heated supports movably disposed within the chamber to support at least two substrates thereon and a contamination collector disposed in communication with the chamber.
Other embodiments of the invention generally provide an apparatus for heating substrates, comprising a chamber having a cavity with at least one cassette having a plurality of heated supports disposed within the cavity to support a plurality of substrates, a heating layer disposed within the cavity and positioned to provide radiant heat to the at least one cassette and a contamination collector for accumulating contaminates from within the chamber.
In another embodiment of the invention, a method for removing contaminates within a chamber, comprising supporting a plurality of substrates on a plurality of heated supports within the chamber, providing a process temperature between about 200xc2x0 C. and about 1000xc2x0 C., providing a vacuum within the chamber and depositing contamination upon a contamination collector coupled to the chamber.